If I place an ‘Attack Target’ flag near a crypt my footmen/knights/etc. move toward it, attack (and kill) the skeletons/zombies, but then ignore all the structures (crypt/fences/etc.).
If I place the ‘Attack Target’ flag directly on the crypt they will wail on it but never destroy it. I can cancel the order or tell them to go somewhere else and they happily leave the crypt alone.